Entrypoints can be trailtlets Configurable

This means a custom proxy can be installed, and configured using traitlets in a standard jupyter_server_config file

jupyter_server_proxy/__init__.py

@@ -2,6 +2,7 @@
 
 from ._version import __version__  # noqa
 from .api import IconHandler, ServersInfoHandler
+from .config import ServerProcess, ServerProcessEntryPoint
 from .config import ServerProxy as ServerProxyConfig
 from .config import get_entrypoint_server_processes, make_handlers, make_server_process
 from .handlers import setup_handlers
@@ -45,7 +46,9 @@ def _load_jupyter_server_extension(nbapp):
         make_server_process(name, server_process_config, serverproxy_config)
         for name, server_process_config in serverproxy_config.servers.items()
     ]
-    server_processes += get_entrypoint_server_processes(serverproxy_config)
+    server_processes += get_entrypoint_server_processes(
+        serverproxy_config, parent=nbapp
+    )
     server_handlers = make_handlers(base_url, server_processes)
     nbapp.web_app.add_handlers(".*", server_handlers)
 
@@ -81,3 +84,5 @@ def _load_jupyter_server_extension(nbapp):
 # For backward compatibility
 load_jupyter_server_extension = _load_jupyter_server_extension
 _jupyter_server_extension_paths = _jupyter_server_extension_points
+
+__all__ = ["ServerProcess", "ServerProcessEntryPoint"]

jupyter_server_proxy/config.py

@@ -76,7 +76,7 @@ def _default_path_info(self):
     )
 
 
-class ServerProcess(Configurable):
+class _ServerProcess(Configurable):
     name = Unicode(help="Name of the server").tag(config=True)
 
     command = List(
@@ -264,6 +264,22 @@ def cats_only(response, path):
     ).tag(config=True)
 
 
+class ServerProcess(_ServerProcess):
+    """
+    A configurable server process for single standalone servers.
+    This is separate from ServerProcessEntryPoint so that we can configure it
+    independently of ServerProcessEntryPoint
+    """
+
+
+class ServerProcessEntryPoint(_ServerProcess):
+    """
+    A ServeProcess entrypoint that is a Configurable.
+    This is separate from ServerProcess so that we can configure it
+    independently of ServerProcess
+    """
+
+
 def _make_proxy_handler(sp: ServerProcess):
     """
     Create an appropriate handler with given parameters
@@ -319,16 +335,23 @@ def get_timeout(self):
     return _Proxy
 
 
-def get_entrypoint_server_processes(serverproxy_config):
+def get_entrypoint_server_processes(serverproxy_config, parent):
     sps = []
     for entry_point in entry_points(group="jupyter_serverproxy_servers"):
         name = entry_point.name
         try:
-            server_process_config = entry_point.load()()
+            server_process_callable = entry_point.load()
+            if issubclass(server_process_callable, ServerProcessEntryPoint):
+                server_process = server_process_callable(name=name, parent=parent)
+                sps.append(server_process)
+            else:
+                server_process_config = server_process_callable()
+                sps.append(
+                    make_server_process(name, server_process_config, serverproxy_config)
+                )
         except Exception as e:
             warn(f"entry_point {name} was unable to be loaded: {str(e)}")
             continue
-        sps.append(make_server_process(name, server_process_config, serverproxy_config))
     return sps
 
 

tests/resources/jupyter_server_config.py

@@ -51,6 +51,12 @@ def my_env():
     return {"MYVAR": "String with escaped {{var}}"}
 
 
+# Traitlets configuration for test-serverprocessentrypoint in the dummyentrypoint package
+c.CustomServerProcessEntryPoint.request_headers_override = {
+    "X-Custom-Header": "custom-configurable"
+}
+
+
 c.ServerProxy.servers = {
     "python-http": {
         "command": [sys.executable, _get_path("httpinfo.py"), "--port={port}"],

tests/test_proxies.py

@@ -528,3 +528,11 @@ async def test_server_proxy_rawsocket(
         await conn.write_message(msg)
         res = await conn.read_message()
         assert res == msg.swapcase()
+
+
+def test_server_configurable_class(a_server_port_and_token: Tuple[int, str]) -> None:
+    PORT, TOKEN = a_server_port_and_token
+    r = request_get(PORT, "/test-serverprocessentrypoint/", TOKEN, host="127.0.0.1")
+    assert r.code == 200
+    s = r.read().decode("ascii")
+    assert "X-Custom-Header: custom-configurable\n" in s